1. Field of the Invention
The present invention relates to a cap for a semiconductor device and, more particularly, to a cap for a semiconductor device having a cap body with which an optical window is sealed by means of a low-melting point glass.
2. Description of the Related Art
A semiconductor device including a laser diode mounted thereon has been conventionally known in the prior art. In such a device, as shown in FIG. 1, a laser diode 30 is mounted on a stem 20 and covered by a semiconductor device cap 10 so that the laser diode is accommodated and hermetically sealed in the cap 10. The semiconductor device cap 10 is made by press-forming a metal plate to form a cap body 12 having a light transmitting opening 12a and adding a light transmitting window 14 made of a glass plate which is sealed to the periphery of the light transmitting opening of the cap body by means of a low-melting point glass 16. In FIG. 1, reference numerals 22 and 24 indicate leads; 26, a glass seal; and 28, a holder for laser diode.
One of conventional methods for sealing the light transmitting window 14 with the cap body 12 is that the cap body 12 is heated in the atmosphere to form an oxidized film on a surface thereof and, then, using the oxidized film the light transmitting window 14 is sealed by means of a low-melting point glass. Another method is that nickel is plated on a surface of the cap body 12 and a Ni—Pb eutectic alloy layer is formed at the time of sealing by an eutectic reaction between a lead component contained in the low-melting point glass and Ni contained in the nickel plated layer, so that the light transmitting window 14 is sealed by means of a low-melting point glass and the eutectic alloy layer.
FIG. 5 is an enlarged view of a sealing portion (A in FIG. 1) in which the light transmitting window 14 is sealed with the cap body using an eutectic reaction between Pb-component contained in the low-melting point glass 16 and Ni in the nickel plated layer 18. In FIG. 3, the reference numeral 12 denotes a metal cap body; 18, a nickel layer plated on the cap body; and 20, an eutectic alloy layer of Ni—Pb.
Recently, however, since it is pointed out that the natural environment is affected by lead and, therefore, not using lead has been promoted in many production processes for various goods. In a method of producing an optical cap for semiconductor device using a low-melting point glass containing lead, using no or little lead has been required. Under such circumstances, there is a proposal to produce an optical cap for semiconductor device using a low-melting point glass containing no lead. For example, in Unexamined Japanese Patent Publication No. 2003-34549, it has been proposed that a glass of SnO—P2O5, containing no lead is used as a sealing glass for sealing a light transmitting window.
In a process for producing a semiconductor device cap in which a laser diode is installed, using no lead has been proposed by using a glass of SnO—P2O5, containing no lead, for sealing the light transmitting window. However, there is a problem that a glass of SnO—P2O5 is not sufficient in moisture resistance and reliability, as a better sealing performance and reliability are required for a sealing cap used in a semiconductor device.